(1) Field of the Invention
This invention relates to a method of manufacturing cationic acrylamide polymers mainly used as paper strength agents and flocculants, said polymers, and the applications of these polymers. More specifically, it relates to cationic acrylamide polymers obtained by carrying out a Hofmann degradation reaction on acrylamide polymers at high temperature for a short time, their method of manufacture and the applications of these polymers.
(2) Description of the Prior Art
Examples of cationic acrylamide polymers (acrylamide polymers are hereafter referred to simply as polyacrylamides) known in the prior art are Hofmann decomposition polyacrylamides, Mannich polyacrylamides, and copolymers of cationic monomers and acrylamides. Some of these polymers have various uses such as paper strength agents and flocculants, while the use of others is being considered.
Hofmann decomposition polyacrylamides have excellent properties not shared by Mannich polyacrylamides and copolymers of cationic monomers, however they lose their cationicity over a period of time in aqueous solution, and their use has therefore been limited.
Various means have been considered to improve the characteristics of these polymers. One such means is to carry out the Hofmann decomposition of polyacrylamides at low temperature in order to suppress side reactions and thereby suppress temporal deterioration. It is reported for example in "Kobunshi Ronbun", Vol. 33, No. 6, pp. 309-316, 1976, that in the Hofmann decomposition of polyacrylamides, substitution of amino groups can occur easily even at low temperature due to the reaction promoting effect of neighbouring groups, and it is also disclosed that to suppress side reactions (such as hydrolysis and formation of lactam rings) and depolymerizations, it is desirable to carry out the reaction at a low temperature of the order of 25.degree. C. or less to obtain amino-substituted PAM (polyacrylamides) with high performance. The advantage of carrying out the Hofmann reaction of polyacrylamides at low temperature is also reported in Japanese Laid-Open Patent Application Nos.61-200103, 58-152004, 58-108206, 57-165404, 55-6556, 52-152493 and 51-122188.
However, according to tests performed by the inventors of the present invention, it was found that merely carrying out the Hofmann reaction at low temperature does not improve the temporal variation to such an extent as to permit commercial application of the polymers. In another approach, hydroxyl-substituted compounds into which cationic groups have been substituted such as quaternary ammonium salts, or N,N-dialkyl substituted diamines, guanidine and polyamines are also present when the Hofmann decomposition is carried out, and these substances are made to react with isocyanate intermediates of the Hofmann decomposition so as to incorporate them in the polymer, thereby preventing temporal variation from occurring, as disclosed in Japanese Laid-Open Patent Application Nos. 62-59602, 61-120807, 57-192408, 56-144295, 54-145790 and 53-109594.
According to the present inventors, however, these methods have still not given satisfactory results.